Insolubilized cellulose ether



Patented Feb. 21, 1950 INSOLUBILIZED CELLULOSE ETHER Alva L. Honk, San Luis Obispo, Calif., and Louis H. Bock, Huntingdon Valley, Pa., assignors to Riihm & Haas Company, Philadelphia, Pa., a

corporation of Delaware No Drawing. Application December 3, 1946,

Serial No. 113,839

This invention deals with a method whereby cellulose is utilized in desired forms or shapes. It concerns a method in which cellulose derivative is rendered soluble and applied or shaped from solution, whereupon the resulting form is rendered insoluble. The invention also concerns the products which are thus obtained. These comprise a cross-linked form of a cellulose ether which is peculiar to this invention.

It has been proposed to convert cellulose to hydroxyethyl cellulose or carboxyalkyl cellulose ethers which are soluble in alkali solutions, deposit modified cellulose therefrom in the form of films or foils, and set the deposited film or foil with acid. Such material, however, remains water-sensitive and capable of re-solution in alkali solutions.

A method has now been found by which a cellulose derivative in a soluble state may be shaped or deposited in a desired form and then rendered insoluble, even in alkaline solutions. This method comprises treating cellulose with an alkali hydroxide to form alkali cellulose, reacting the alkali cellulose with isobutylene oxide to form an alkali-soluble product, forming a solution thereof in an alkali solution, forming a desired shape or form therefrom, removing alkali from said shape or form, treating it with a soluble cobalt salt, and heating the thus treated shape or form to insolu bilize the cellulosic material.

The cellulose may thus be formed as a coating or film, as on a woven or knitted fabric, or it may be cast as an integral object, such as a foil or unsupported film. The coating is useful as a textile finish, for example, while the film may be used as a modified cellulose sheet or other formed cellulosic object.

As a source of cellulose for use in this process, there may be used cotton linters, purified wood pulp, rayon waste, or the like.

When cellulose is treated with a solution of a strong alkali, it is converted at least in part to so-called alkali-cellulose. For this purpose, there may be used relatively strong solutions of sodium hydroxide, potassium hydroxide, or strong quaternary ammonium hydroxides such as benzyl trimethyl ammonium hydroxide or dibenzyl dimethyl ammonium hydroxide. Alkali solutions of 10% up to 50% or more may be used. Although the conversion to alkali cellulose is rapid, it is often desirable to allow the alkali cellulose to age in a closed container. An inert atmosphere improves the nature of the final product.

Excess alkali may be removed, as by draining 2 Claims. (Cl. 260-232) or centrifuging, if desired, although this is not essential.

Isobutylene oxide is then reacted with the alkali cellulose. This reaction may be accelerated by warming, temperatures from 20 C. to C. being useful, 25 C. to 40 C. being preferred. When about 0.05 to about 0.5 mol of isobutylene oxide has reacted per glucose unit, the cellulose becomes soluble in solutions of about 5% to about 15% of a strong alkali, such as sodium hydroxide.

This solution may be applied to a textile base to form a coating thereon. The alkali may be destroyed with acid, a dilute solution such as a 2% to 10% solution of acetic or sulfuric acid being effective in destroying the alkali and depositing the cellulosic material. Instead of a coating, a foil may be formed by deposition of solution on a metal or ceramic ware plate or roll. Similarly, the cellulosic material may be formed as a filament rod or other shaped object by in jection into an acidic coagulating bath, or solid objects 'may be cast by other methods. The formed or shaped objects at this stage are still water-sensitive and capable of being redissolved by a strong alkali in solution.

The formed or shaped object may, however, now be rendered insoluble by treatment with a cobalt salt, which is most readily applied from about 0.05% to about 4% aqueous solution of such salts as cobalt chloride, cobalt nitrate, or cobalt acetate, followed by heating. At temperatures of to C., the cellulosic materials become quite insoluble in four hours to less than one hour.

I In the application of a cobalt salt, the use of a buffering salt, such as sodium or potassium acetate, is helpful in controlling the conditions of reaction. A high concentration of cobalt hastens the insolubilizing action but may cause dry strength of the product to be slightly decreased. The presence of sodium acetate as a typical buffer in a molecular proportion from about 0.5 toabout 0.9 that of the concentration of the cobalt salt gives a good balance and assures insolubilizing action without deleterious action of cobalt on cellulose.

The process of this invention is illustrated by the following typical preparations.

- Example 1 tainer for forty-four hours at about 30 C. It was then placed in a Werner-Pfieiderer mixer and treated with 144 parts of isobutylene oxide. The resulting mixture was worked at 38-40 C. for six hours and left standing for fifteen hours with the temperature-between 38 and 30 C. This product was washed with a 50% methanol solution until caustic was removed and, after being dried, was obtained in the form of white flakes. A solution was prepared from. these by suspending 160 parts of fiakes in 1840 parts of 8% sodium hydroxide solution and reducing the temperature of the suspension t.o.- C. Asyrupy, water-white solution resulted.

This solution was poured over a glass plate, which was then passed under a doctor blade set at twenty-four mils clearance. The film on the plate was dried, whereafter the alkali was destroyed in the dried film by immersion in a 5 hydrocarbon acid solution. The film was then stripped from the plate and out into sections. Some of these were dried and then heated in .an oven at 135 C. for four hours. Other were, dipped into a 0.5% cobalt chloride solution and then dried and heated at 135 C. for four hours.

After the various strips had been conditioned at 21 C. in an atmosphere at 65% relative humidity, tensile strengths were determined. Strips dried but not heated and strips dried and heated, all without catalyst, showed tensile strengths of about nine kilograms per square. millimeter when dry and about 0.3 kilogramflper square millimeter when wet. After immersionof strips in the cobalt solution, there was no significant change upon drying at 21 C... but the strips heated at 135 C. had tensile strengths of about eight kilograms per square millimeterwhen dry and 2.2 kilograms per square millimeter when wet. This was about a seven-fold increase in wet strength.

Example 2" As another example illustrating this invention, one hundred seventy parts of a-GQHDJOSE- was mixed with four hundred parts of 20 aqueous sodium hydroxide solution, and this mixture was aged for thirty-six hours in a closed container at room temperature. Thereto seventy-twoparts of isobutylene oxide was added and mixed in a. Werner-Pfieiderer mixer at 21 C. for six hours The reaction mixture was then left standing overnight and washed with about 120 parts of acetic acid diluted with 120 parts of water. The insoluble portions was washed with water until free from acetic acid and driedat. room temperature.

A portion of eighty parts of the dried product was dissolved in 920 parts of 8% sodiumhydroxide solution. After this mixture had been chilled to -5 C., a clear solution was obtained havinga viscosity of 2500 centipoises.

The solution was forced through an orifice 0.25" x 0.03" into a bath composed of suljfuric acid, 8% of sodium sulfate, 5% of glucose, and 1.0% of cobalt chloride (C0Cl2'H2O) and the cellulose ether was thus coagulated or precipitated in the form of a ribbon. This ribbon was washed with water, dried, and baked at about 130 C. for about four hours. A water and alkaliinsoluble product was thus obtained.

Example 3 One hundred seventy parts of a purified a-cellulose and four hundred parts of sodiumhydroxide solution were mixed and allowed; to stand in a closed container at 30 for twenty-four. hours. Themixture was then Placed in a Werner-Pfleiderer mixer, and 144 parts of isobutylene oxide was added and mixed at 40 C. for six hours. The batch was then neutralized by addition of 10% acetic acid, which resulted in the precipitation of the hydroxyisobutyl ether of cellulose. This was washed thoroughly with water and dried in an oven at C. There was obtained 184 parts of a white fiaky solid which, according to analysis, contained 445.2% carbon and 6.46% hydrogen. This corresponds to about 0.08 hydroxyisobutyl group per glucose unit. A solution was prepared by suspending 160 parts of dried flakes in 1840 parts' of 8% sodium hydroxide solution and chilling to 0 to 5 C. The resulting solution was a syrupy, water-white solution having a viscosity of 9,50 centipoises.

The preparation of films was done by spinning the above solution through a slit 0.01 by 0.25 into a bath having the followin composition:

15% sulfuric acid 8% sodium sulfite 5% corn syrup 72% water The ribbon obtained was washed thoroughly and then soaked for one hour in a solution containing-4.0% cobaltous chloride hexahydrate and 1.0 sodium acetate. The films were suspended on a. frame so that they could shrink in only the transverse direction and were dried at room temperature and then cured by being-placed in an oven at 150 C; for two hours. The dry film had cross-sectional dimensions of'0.89 mm. x .037 mm. The dry tensilestrength was 10.1 kilograms per square millimeter. The wet strength was 3.3 kilograms per square millimeter.

Example 4 As ,yet another example of the preparation of the products of this invention, 170 parts of purifiedcellulose was taken up in four hundred parts of a 20% caustic soda solution and aged twentyfour hours in a closed vessel. Thereupon, 108 parts. of isobutylene oxide was run in and the mixture worked mechanically for six hours at 40 C. in a, closed Werner-Pfleiderer mixer. The material was left standing overnight. It was then washed with methanol to remove excess alkali and dissolved in an 8% caustic soda solution. Analysis of the solid cellulose ether showed the presence of 0.08 hydroxyisobutyl group per glucose unit.

The solution was forced through an orifice as in theprevious example into a similar acid bath containing about. 2% of cobalt chloride. After the ribbon was washed and dried, it was baked atl-40 C; for two hours. The, product was insoluble in sodium hydroxide solutions.

We claim:

1. Aprocess for insolubilizing an alkali-soluble cellulose ether formed by reacting alkali cellulose with, isobutyleneoxide and removing alkali therefrom. which comprises treating said cellulose ether with a, solution of a water-soluble cobalt salt. and heatingthe thus-treated cellulose ether at to C. until the said ether is insoluble.

2. A process for insolubilizingan alkali-soluble cellulose, ether prepared-by reacting an alkali cellulose with-0.2 'to -0-.8 mole, of isobutyleneoxide per glucose, unit of the cellulose and removing alkali therefrom, which comprises treating said cellulose other with 0.04% to 4%; aqueous'solution of a 75 soluble cobaltsalt andheating. the thus-treated ceiiulose ether at a temperature of 120 to 150 C. until insoluble.

The following references are of record in the file of this patent:

UNITED STATES PATENTS L HOUK Number Name Date LOUIS 309 1,920,297 Dykstra Aug. 1, 1933 2,086,419 Hunt et a1 July 6, 1937 REFERENCES CITED 2,265,919 Lillienfeld Dec. 9, 1941 2,455,083 Musser Nov. 30, 1948 Certificate of Correction Patent No. 2,498,208 February 21, 1950 ALVA L. HOUK ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 3, line 20, for the Word ydrocarbon read hydrochloric; line 23, for Other read Others; line 53, for portions read portion; line 63, for (CoCl -H O) read (COCZ -GH O); column 4, line 9, for 445.2% read 45.2%;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 23rd day of May, A. D. 1950.

THOMAS F. MURPHY,

Assistant Gammz'ssz'oner of Patents. 

1. A PROCESS FOR INSOLUBILIZING AN ALKALI-SOLUBLE CELLULOSE ETHER FORMED BY REACTING ALKALI CELLULOSE WITH ISOBUTYLENE OXIDE AND REMOVING ALKALI THEREFROM, WHICH COMPRISES TREATING SAID CELLULOSE ETHER WITH A SOLUTION OF A WATER-SOLUBLE COBALT SALT AND HEATING THE THUS-TREATED CELLULOSE ETHER AT 120* TO 150*C. UNTIL THE SAID ETHER IS INSOLUBLE. 